The amphetamine derivative 3,4-methylenedioxymethamphetamine (MDMA) is a potent monoaminergic neurotoxin with the potential to cause serotonergic neurotoxicity, but has become a popular recreational drug. Little has been known about the cellular effects induced by MDMA. This report shows that MDMA inhibits neuronal cell growth and differentiation. MDMA suppressed neuronal cell growth. The results of quantitative real-time PCR analysis showed that Egr-1 expression is elevated in mouse embryo and neuroblastoma cells after MDMA treatment. Transiently transfected Egr-1 interfered with the neuronal differentiation of neuroblastoma cells such as SH-SY5Y and PC12 cells. These findings provide evidence that the abuse of MDMA during pregnancy may impair neuronal development via an induction of Egr-1 over-expression.